This application is an improvement upon the invention described and illustrated in copending, commonly owned application Ser. No. 251,358, filed May 8, 1972, now U.S. Pat. No. 3,832,118.
The subject matter of said copending application Ser. No. 251,358 is hereby incorporated herein by reference.
This invention relates to the manufacture of shaped cast concrete structural members which may take the form of rectangular slabs, T-slabs or multiple T-slabs. In the interest of brevity, such shaped structural members are hereinafter referred to generally as slabs.
In the casting of concrete slabs, mold forms are employed which are open at the top for reception of the fluid concrete mix. When the fluid concrete mix is set and the cast product is to be removed from the mold, it must be possible to establish clearance betwen the product and the sidewalls of the mold to strip the product therefrom. This stripping clearance heretofore has been obtained by a variety of ways.
One particularly advantageous arrangement is described in the aforementioned pending application Ser. No. 251,358 wherein the side members are sprung away after casting by a cam mechanism disposed beneath the mold form.
In the fabrication of cast concrete structural members by apparatus such as described in the aforementioned copending application Ser. No. 251,358, prior to the raising of the cast slab out of its form, the side walls of the form must be separated from the sides of the slab. This is accomplished in the apparatus of the copending application by means of a cam arrangement shown therein in FIG. 7. This cam arrangement includes a flat cam plate having pairs of oppositely oriented slots within which are received pins depending from the vertical sides of the mold form. The force exerted on pin members by the sides of adjacent slots as the cam plate is displaced, causes the pins to be displaced and a corresponding movement is translated to the sides of the mold form.
While the foregoing cam arrangement provides an effective means of springing the side members of the form from the cast stem, it is subject to serious disadvantages. For example, because of the adhesive forces existing between the forms and the concrete, large forces must be developed to effect separation thereof. These forces are translated through the slot edges and pin members resulting in rapid wear of the elements unless resort is made to heavy structural members. This in turn undesirably increases the cost of the form.
Another disadvantage of the aforementioned copending application Ser. No. 215,358 is that the ball member cam follower of elevating mechanism concentrates the weight of the concrete over a small area and the resultant sliding friction between the cam follower and cam causes rapid wear of the elements. To this end, it should be appreciated that when casting structural members in a form which extends 500 feet in length, the total weight of the cast member may approach 180,000 pounds.
These disadvantages are overcome by the present invention which is particularly concerned with improvements upon the side wall springing mechanism and elevating mechanism of the apparatus shown and described in the aforementioned copending application Ser. No. 251,358, to enable the production of slabs more efficiently and more economically and which provides a greater flexibility in the utilization of the apparatus.
Another problem encountered with forms for casting slabs in slurry leakage frequently occurs at the mating edges of the side members of the form and the pallet. Such leakage results in discoloration and/or flashing of the cast product or the formation of "icicles" which make the product unacceptable without further and costly steps.
The problem becomes particularly noticeable in the fabrication of slabs wherein the horizontal pallet is adjustable in height between the side members of the form. A height adjustment of the pallet is extremely desirable in order to accomodate the form to the fabrication of slabs of various sizes and provides a distinct advantage over conventional slab construction wherein the pallet of the form is blocked up to fabricate slabs with a desired length of stem. However, inasmuch as the sides of the form have a small gradually increasing taper, a small leakage space results when the pallet is elevated substantially within the sides of the form, as would be the case when fabricating a short stem T-slab. Further, because holding means are generally provided at the lower end of the form sides, there is a tendency for the sides to bow because of the resiliency of the relatively thin sides of the form. This bowing is further aggravated by the weight of wet concrete. Resort to the use of conventional sealing gaskets along the edges of the pallet is ineffectual to compensate for the bowing effect and resultant leakage. In accordance with the present invention, this leakage problem is overcome by resort to the use of a resilient, expandable pallet which allows a greater latitude of height adjustment.